The present invention relates to conveyor rollers of the type which rotate on fixed axles or shafts and have internally mounted bearings at each end, and more particularly relates to conveyor rollers suitable for use where dust and moisture create a corrosive environment, yet conveyor cleanliness is of prime concern.
Examples of applications for the aforementioned type of conveyor rollers include food and beverage handling facilities. In such applications, under normal operating conditions, each roller is subjected to periodic loading and subsequent axle misalignment as a package travels across a conveyor. However, during periods of increased production, each roller may be subjected to higher speeds and almost continual load and axle misalignment.
Conventional conveyor rollers utilize metallic journal bearings, sleeve bearings, or antifriction bearings such as ball bearings which are subject to misalignment or a loss of bearing surface contact when the roller axle deflects under heavy and/or impact loads. Bearings may "walk" or move within the roller under these overload conditions. In the case of ball bearings, a deflection of the roller axle of only 11/2.degree. causes the individual balls to become pinched between the inner and outer races. This additional load on the bearing causes a significant increase in friction as well as a corresponding increase in roller temperature. Conveyor roller bearings deteriorate much faster during extended periods of this type of axle deflection. An additional problem occurs when using powered or driven rollers having grooves in which the drive belts ride. Forming these grooves may overstress the rollers and can undesirably preload the bearing when it is inserted in the end of the roller. Other preloading may result due to the manufacturing of the inner roller surface. Such preloading accelerates friction, wear and lockup of the bearing.
An additional drawback of conventional conveyor rollers is the clattering din they produce during periods of peak production which is quite objectionable. Increased legislative regulation of worker health and safety has given the goal of eliminating excessive noise.
Rollers have been constructed with polymeric material, however, the mere substitution of polymers for conventional metallic rollers and bearings has generated new difficulties, such as the inability of polymeric bearings to withstand insulative heat generated by friction produced during roller operation. Such heat buildup can accelerate friction, wear and lockup of the bearing.
An additional problem arises when utilizing axle supported rollers in wide conveyor applications where flexible items such as wide belts, paneling, film or strip material, and paper are conveyed. In such applications, it has been found desirable to employ flexible, polymeric rollers which provide an anti-static carrying surface for the conveyed sheet-like items, but use of the wide polymeric roller creates a sagging or drooping in the central portion of the roller due to the combined weight of the roller and its support axle. This sagging will cause the material being conveyed to erratically seek the higher portions of the roller where the material can be damaged at its sides by the structural framework of the conveyor. In addition, the support axle for the roller is subject to serious misalignment thus causing friction, wear and potential stoppage.
Thus, there is a definite need for a conveyor roller and bearing arrangement capable of low friction operation which cushions and absorbs roller and axle misalignment and keeps rolling friction losses to a minimum. There is also a need for a conveyor roller and bearing arrangement which compensates for normal manufacturing tolerances of the inner surface of the roller in order to avoid preloading the bearing excessively.
It is therefore a major objective of the present invention to provide a conveyor roller designed to rotate on a fixed axle and having internally mounted bearings capable of accepting the maximum of normally encountered axle misalignment without suffering a loss in bearing surface contact and a concomitant increase in friction.
Another objective of the present invention is to provide a conveyor roller bearing designed to generate a minimum amount of excess heat and to readily dissipate whatever amount of heat is generated.
It is a further objective of the invention to provide as internally and externally supported conveyor roller designed to substantially reduce the bending impulse or sagging in the central portion of a wide conveyor roller.
A still further objective of the present invention is to provide a conveyor roller which generates a minimum of operational noise.
Another objective of the present invention is to provide a conveyor roller which is self-lubricated.